Name

gl_InstanceID — contains the index of the current primitive in an instanced draw command

Declaration

in highp int gl_InstanceID ;

Description

gl_InstanceID is a vertex language input variable that
holds the integer index of the current primitive in an instanced draw
command such as glDrawArraysInstanced. If the current
primitive does not originate from an instanced draw command, the value
of gl_InstanceID is zero.